1. Field of the Invention
The present invention relates to a quaternary ammonium salt compound, a composition for forming a resist under layer film containing the same, and a patterning process using the same.
2. Description of the Related Art
In 1980s, photo-exposure using a g-beam (436 nm) or an i-beam (365 nm) of a mercury lamp as a light source had been widely used in the resist patterning. As a means for finer patterning, shifting to a exposure light having shorter wavelength was assumed to be effective, so that, for the mass production process of DRAM (Dynamic Random Access Memory) with 64 MB (work size of 0.25 μm or less) in 1990s and later ones, a KrF excimer laser (248 nm), whose wavelength is shorter than the i-beam (365 nm), had been used in place of the i-beam as the exposure light source. However, for production of DRAM with integration of 256 MB and 1 GB or higher requiring further finer processing technologies (work size of 0.2 μm or less), a light source with a shorter wavelength was required, and thus, a photolithography using an ArF excimer laser (193 nm) has been investigated seriously over a decade.
It was expected at first that the ArF lithography would be applied to the fabrication of 180 nm-node devices. However, the KrF excimer lithography survived to the mass production of 130 nm-node devices, so that a full-fledged application of the ArF lithography started from the 90 nm-node. Furthermore, mass production of the 65 nm-node devices is now underway by combining the ArF lithography with a lens having an increased numerical aperture (NA) of 0.9. For the next 45 nm-node devices, further shortening the wavelength of exposure light is progressing, and the F2 lithography with 157 nm wavelength became a candidate.
However, there are many problems in the F2 lithography: cost-up of a scanner due to use of the large quantities of the expensive CaF2 single crystal for a projection lens; extremely poor durability of a soft pellicle, which leads to change of an optical system due to introduction of a hard pellicle; decrease in etching resistance of a resist film, and so forth. Because of these problems, development of the F2 lithography was suspended, and the ArF immersion lithography was introduced.
In the ArF immersion lithography, water having refractive index of 1.44 is introduced between a projection lens and a wafer by a partial fill method, thereby enabling high speed scanning, and thus, mass production of the 45 nm-node devices is now underway by using a lens with a NA of 1.3.
For the 32 nm-node lithography, lithography with an Extreme-ultraviolet beam (EUV) of 13.5 nm wavelength is considered to be a candidate. Problems to be solved in the EUV lithography are to obtain a higher output power of the laser, a higher sensitivity of the resist film, a higher resolution, a lower line edge roughness (LER), a non-defect MoSi laminate mask, a lower aberration of the reflective mirror, and so forth; and thus, there are innumerable problems to be solved.
Development of the immersion lithography with a high refractive index, another candidate for the 32 nm-node, was suspended because transmittance of LUAG, a candidate for a high refractive index lens, is low, and refractive index of the liquid could not reach an aimed value of 1.8.
As mentioned above, in the photo-exposure used as a general technology, resolution based on the wavelength of the light source is approaching to its inherent limit. Thus, in recent years, patterning through negative tone by organic solvent development that can form a very fine hole pattern, which is not achievable by conventional patterning through positive tone by alkaline development, attracted attention again. This is a process for forming a negative pattern by using a positive resist composition featuring a high resolution by organic solvent development. Furthermore, an attempt to double a resolution by combining two developments, alkaline development and organic solvent development, is under study (Patent Documents 1 to 3).
A multilayer resist method is one of the methods for transferring a lithography pattern to a substrate. In this method, an intermediate film (e.g. a silicon-containing resist under layer film) having etching selectivity different from that of a photoresist film, i.e. a resist upper layer film, is interposed between the resist upper layer film and a substrate to be processed, a pattern is formed to the resist upper layer film, and the pattern is then transferred to the resist under layer film by dry etching using the upper layer resist pattern as a dry etching mask, and further the pattern is transferred to the substrate to be processed by dry etching using the resist under layer film as a dry etching mask.
As a material to be used for such a multilayer resist method, a composition for forming a silicon-containing film has been well known. For example, a silicon-containing inorganic film formed by a CVD method such as a SiO2 film (Patent Document 4) and a SiON film (Patent Document 5), and a material that can be obtained by spin-coating such as a SOG (spin-on-glass) film (Patent Document 6) and a cross-linkable silsesquioxane film (Patent Document 7) may be mentioned.